Vinylidene fluoride (VDF) polymers are known in the art to be suitable as binders for the manufacture of electrodes for use in non-aqueous-type electrochemical devices such as batteries, preferably secondary batteries, and electric double layer capacitors.
Generally, techniques for manufacturing electrodes involve the use of organic solvents such as N-methyl-2-pyrrolidone (NMP) for dissolving VDF polymer binders and homogenizing them with a powdery electrode material and all other suitable components to produce a paste to be applied to a metal collector.
The role of the organic solvent is typically to dissolve the VDF polymer in order to bind the powdery electrode material particles to each together and to the metal collector upon evaporation of the organic solvent.
Nevertheless, more recently, approaches are pursued wherein use of organic solvents is commonly avoided so as to ensure more environmentally friendly techniques, and waterborne solutions have been proposed.
Nevertheless, cathode materials are generally sensitive to moisture because of solubility in water of the same and/or possibly hydrolysis phenomena leading to complete decomposition of the material, which negatively affects final electrode performances. Thus, the water-borne route for manufacturing electrodes may lead to poorer final battery performances or can even be an absolutely non practicable solution, when solubility and/or decomposition is at issue, because of the unavoidable presence of moisture introduced during manufacture of the electrode itself, which might aggress the active material at the high temperatures of typical operations.
On the other side, techniques involving the coating or plating of positive (cathode) electrode materials for improving their performances in Li batteries, including embodiments wherein the same are used for formulating cathodes including a PVDF binder, are already known in the art.
For instance, US 2002/076486 (SAMSUNG SDI CO., LTD.) 20 Jun. 2002 discloses a method for coating a positive electrode material including mixing and drying simultaneously a composition comprising a cathode active material and a coating precursor in a liquid medium. The liquid medium can be either water or an organic solvent such as an alcohol. The coating element is any of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, preferably Al or B. The coated materials are used for fabricating electrodes from a paste comprising PVDF in NMP.
There is thus still a shortfall in the art for electrode-forming compositions providing electrodes showing excellent performances during operation in electrochemical devices, with no negative impact due to moisture uptake of the active electrode material.